The present invention relates to a method and apparatus for real-time analysis of chemical, biological and explosive substances in the air.
Known devices for detecting individual dangerous substances generally have a closed sample chamber for analyzing the substances, and the analysis itself takes several minutes. Devices for the detection of bacteria, viruses or other microparticles provide, for example, for filtering-out and marking of the corresponding particles before the latter can than be detected automatically.
German Patent Document DE 103 06 900 A1 discloses a spectrometer having a laser arrangement for analyzing gas. The spectrometer comprises a chamber for receiving a gas, a device for generating a potential drop in the chamber, a laser light source as well as an optical resonator which is formed by opposing mirrors or is constructed as a ring resonator. Inside the chamber, a laser beam is generated for ionizing the gas. An ion collector is used for the detection of accelerated ions.
A similar device is described in German Patent Document DE 102 47 272 A1, in which, however, instead of an optical resonator constructed by opposing mirrors, a multireflection cell is provided which has mirrors that are constructed such that the laser beam is reflected many times between the mirrors. As a result, the distance of the laser beam interacting with the gas is increased, which leads to a higher current at the ion collector. Because of the optical arrangement generated by means of the mirrors, a plurality of laser beams are formed which each extend between two reflection points, mutually intersect in a central area and fan out toward the mirrors.
One disadvantage of the known state of the art is that, as a rule, only one of many dangerous substance classes is covered by each of the respective devices. Furthermore, the known devices are not capable of detecting the substances directly from ambient air, without pre-enrichment. Moreover, the conventional sampling times, which are in the minutes range, cannot be used for certain applications, such as transit controls, portal monitoring, hazard monitoring, etc. In addition, the known solutions are frequently heavy and bulky have a high initial costs.
One object of the invention therefore, is to provide an improved device for real-time analysis of chemical, biological and explosive substances, in which dangerous substances, such as biopathogens, viruses, bacteria, spores, chemical warfare agents, explosives, toxic compounds and drugs can be detected and proven rapidly and precisely, in ambient air.
According to the invention, this object is achieved by the method and apparatus for real-time analysis of chemical, biological and explosive substances in the air according to the invention, which includes at least a gas analysis sensor, a fluorescence/luminescence sensor and a sensor for determining the size and number of particles. The sensors are each connected with a multireflection cell as an open measuring path, and the device also includes an evaluation unit.
As a result, the disadvantages of the state of the art techniques are avoided, and an improved solution is provided for real-time analysis of chemical, biological and explosive substances in the air. In particular, the invention rapidly and precisely detects and proves dangerous substances, such as biopathogens, viruses, bacteria, spores, chemical warfare agents, explosives, toxic compounds and drugs in the ambient air. The number of pathogens or radioactive particles can easily be determined. The invention thus achieves a relative concentration measurement which cannot be determined by means of state of the art sensors. Furthermore, the threat class types can be determined based on the ratio of dimensions, fluorescence signals and gaseous constituents of the measured particles.
One of the measurement principles of the present invention is based on spectroscopic gas sensor technology, which operates using the speed of ions during their movement under the influence of an electric drift field in the air. Based on the different mass and cross-section of the ions, it is possible to differentiate between individual substances. The signal is measured as an arrival time spectrum of different types of ions, as in time-of-flight spectroscopy, but without the requirement of bulky instrumentation, vacuum pumps, etc.
Such ion mobility spectroscopy (IMS) can be used for the present invention. Most known instruments used for this purpose operate by means of a membrane inlet system and radioactive ion sources. This protects the instruments against water, vapor and all other conceivable contaminations in the air. The ionization principle utilized by these known instruments is based on a charge transfer reaction mechanism, which is also called chemical ionization.
An important element of the present invention is the combination of a highly sensitive ion detection device with a highly selective laser-based ionization mechanism. The ionization process itself is a two-photon ionization step leading to a detailed ion spectrum which permits better selectivity of the ion formation stage and better sensitivity, down to the ppt (parts per trillion) range.
The analysis part of the ion mobility spectroscopy instrumentation is used to detect enzymatic reaction products, pyrolysis starting materials of biomolecules or chemicals of toxins.
On the other hand, each biological system or molecule in living cells exhibits a fluorescing reaction when it is irradiated by UV light. As a result, a component of the bio-aerosol detection device according to the present invention, specifically a tunable laser ionization source (TULIS), offers an excellent possibility for detecting the fluorescent reaction mechanisms in living cells.
Finally, the intense laser irradiation and the long measuring path of the device according to the invention offer a simple possibility of measuring light reflections of particles, that is, the backscatter. This signal can be used for detecting the number and the size of the particles.
The combination of the above-mentioned measuring systems is a part of the present invention. In particular, the invention includes: i) a miniaturized ion mobility sensor for detecting gaseous or chemical compositions; ii) a fluorescence unit for detecting biomolecules; and iii) a backscatter detection unit for detecting the number and the size of particles. A multireflection cell with a miniaturized tunable laser source forms a combining element of these components. The measuring unit is an open system, in which no delays occur between the sampling and the analysis.
The combination and integration of CCDs, the ion mobility spectrometer, the multireflection cell and the laser leads to a compact and integrated device.
The multireflection cell (multipass laser cell—MLC) is the sampling and connection point of the gas analysis sensor (IMS), of the fluorescence and/or luminescence sensor and of the sensor for measuring the particle size and the particle number. A laser beam is introduced into the multireflection cell, whose beam path is lengthened by several internal reflections between two mirrors.
The length of the multireflection cell is approximately 9 centimeters. The length of the beam path is increased to approximately 3 to 9 meters as a result of the mirrors, without major losses. The wavelength of the laser irradiation source which is used amounts to between 200 nm and 350 nm (preferably 260 nm to 270 nm), with a repetition frequency of 10 Hz to 50 Hz. The pulse duration of the laser source amounts to 2 ns, and the mean pulse energy is at approximately 60 μJ. For example, a passive Q-switched diode pump solid-state laser for the stimulation and ionization can be used as the laser irradiation source.
A miniaturized ion mobility spectrometer, which operates in linear and low-field regions, is connected with the multireflection cell. By using low-field IMS technology, shorter measuring times and more detailed spectra are achieved in comparison with the intense-field IMS technology. Because of the excellent signal-to-noise ratio, measurements of sub “parts per trillion” (ppt) can easily be achieved.
In addition, by using a selective two-photon-driven ionization process, a higher sensitivity and a significant reduction of undesirable influences can be achieved. This is an important component of the analysis part. The invention can thereby operate in a so-called open system without membranes or separation processes. As a result, higher sensitivity can be achieved relative to known systems, with low crossover influences and a real-time measurement.
According to the invention, the laser emits infrared radiation which, however, extends into the UV range, by means of frequency modulation techniques. With an optical quasi-continuous wave output of more than 1.5 mW, the laser irradiation source is sufficient for detecting biological substances.
When the laser beam stimulates a photon absorption in the multireflection cell, the intensity of the emitted fluorescence signals is collected in a photo diode detection unit by way of suitable filters for the elimination of scattered light. When using a tunable laser, adjustable liquid-crystal filters (LCTFs) or spectrometers can be used to increase the output and achieve higher resolution.
Furthermore, improved detection characteristics can be achieved by the use of fluorochromes in connection with antibodies. Fluorochromes are fluorescing markers of a high quantum and stokes efficiency. Stokes efficiency means that the change between the stimulation wavelength and the emission wavelength is high; for example, up to 200 nm. As a result the filtering between the stimulation wavelength and the emission wavelength is clearly facilitated.
A particle backscatter sensor is combined with the multireflection cell because particles, aerosols, bacteria and spores generate an intensive backscatter signal when they meet the laser beam.
Because of the long beam path, a large number of reflection signals are generated perpendicular to the laser beam. Together with a CCD detector element, the particle size and number are determined therefrom. Furthermore, so-called “particle image velocimetry” (PIV) can be used. This software takes snapshots of the particle position at different times and computes a velocity model therefrom. PIV can be used for regulating and measuring the examined airflow and for computing the population numbers.
Volatiles of toxins (aerosol) or other types can be detected by means of the ion mobility spectroscopy analysis device. In addition to a specific drift time, a substance-selective ionization process results in a real-time measurement with an increases resolution of the examined process.
Spores and bacteria can be detected by way of released volatiles of a pyrolysis reaction which occurs when the intense green or IR laser light is emitted into the MCL cell. For a better differentiation, the laser light can be supplied in a permanent or switched manner. Even smaller pyrolysis products of bacteria cell membranes can be detected in this fashion. Detectable volatiles may be ammonia and orthonitrophenols (ONP). Spores are detected by the observation of calcium dipicolinate (DPA content 5-15%) or picolinic acid (PA). The measurement can take place by means of ion mobility spectroscopy or fluorescing parts.
In the case of particle size species, such as bacteria, spores and aerosol, the laser irradiation is reflected and is detected by way of backscatter signals (LIDAR). The size and the number of the observed particles can then be used to differentiate, and an alarm is triggered starting at a certain threshold value.
Since viruses are small species of a size of between 10 and 300 nm, detection by using scattered signals is difficult. To detect viruses, they are charged with a voltage or are ionized by means of a laser source, so that they can be identified separately and by the electronic drift field of the ion mobility spectroscopy device.
Most biological warfare (BW) pathogens preferably have a geometry which enables them to spread in the environment. These drop-shaped suspended substances usually have a size of between 0.5-5 μm. In addition to these pathogens, there are further substances, such as stabilizers, solvents or additional chemicals. A large range of BW pathogens are identified by means of known solvents and chemicals according to a typical pattern.
An integrated electronic identification and interface module, which is provided for each of the corresponding sensors, operates while interacting with hardware coordinated with a signal processor and signal evaluation algorithms.
In ion mobility spectroscopy, measurements can be made down to a level which permits detections in the range of ppt. The signal to noise factors are in the low ppb range at approximately 100, and can easily be intensified by an algorithm. The concentration originating from BW is high, particularly when using our laser-desorbing phase of the vaporization.
Detection with a high sensitivity in the particle phase has three parts. The first is the intense laser irradiation together with the short distance to the starting point from which the measurement takes place—a circumstance which ensures overall good detection while interacting with the sensitivity. The second is the velocity measurement; and the third is based on the currently used short wavelength emanating from the radiation source, so that good sensitivity is also achieved during the detection of even small particles.
Due to the targeted use of a two-photon-driven stimulation, a much higher quantum gain is achieved than can be achieved when a stimulation is used that is driven by one photon.
Because of the resonance-amplified multiple-photon ionization (REMPI), the sensitivity of the ion mobility spectroscopy based on the laser is greater than in the case of those of the conventional type. As required, this can by further amplified by two or three color ionization processes.
By using different wavelengths to illuminate the particles, an effective change is carried out during differentiation of various types by means of the size and arrangement. In addition, high-resolution CCDs are used to receive the backscatter signals from different angles in order to obtain a multidimensional overall picture.
The use of a resonant two-photon-driven stimulation achieves better sensitivity than when non-resonant single-photon-driven stimulation steps are used. Furthermore, the pulsating feeding reduces the problems of overlapping with respect to the wavelengths of feeding and emission.
As mentioned above, the measuring time during the ion mobility spectroscopy detection is brief; the excellent signal-to-noise ratio leads to a so-called “single shut measure frame” (a measurement with a one-time exposure). This means that a measurement for the detection of the spectra takes 20 ms. Moreover, particle identification takes place very rapidly (<1 ms) and is only a function of the used CCD technology. For example, a CCD array can be used. Fluorescence detection is also very rapid (<20 ms) and is a function of the usable CCD and duplication/identification technique.
For all sensors, the repetition rates for the detection are between 25 ms up to 100 ms. This means that the longest measuring time is 100 ms; the shortest measuring time is 25 ms. Compared to the demanded measuring time (less than 1 min), these time frames have the result that between 600 and 2,400 measurements can be carried out per minute, achieving a significant breakthrough in improving signal systems and accumulation routines.
In addition, a nuclear radiation sensor may also be provided for detecting radioactive emissions, and may be constructed as a very small silicon drift detector.
Finally, a process according to the invention for the real-time analysis of chemical, biological, explosive and/or radioactive substances in the air by means of a device according to claim 1 has the following steps:                UV laser irradiation of a sample in the multireflection cell;        ionization of the sample, if possible, detecting of the charge, the mobility and the wavelength;        fluorescence measurement of the sample, if possible, detection of the color, the duration and the wavelength;        backscatter measurement of the sample, if possible, detection of the particle number and the particle size.        
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.